Aquifers are being overexploited in major food-producing regions, including the North China Plain, a region that yields half of China’s wheat and one third of its corn; Punjab, Haryana, and other highly productive agricultural states in northern India; and the southern Great Plains of the United States, a major grain-producing region. Together, China, India, and the United States produce nearly half the world’s grain, and these three countries plus Pakistan collectively account for over three fourths of the world’s reported groundwater extraction for agricultural purposes. Falling water tables in these countries may make expanding world food production more difficult.